A number of devices have been developed to enhance the taste and aesthetic quality of food cooked in microwave ovens either by ensuring uniform heat circulation (U.S. Pat. No. 4,121,510), by browning and searing foods through creating and control of electrical fields using conductive metals (U.S. Pat. No. 3,946,187) or by converting microwave energy, by way of a resistive film, to heat energy which is transferred to the food surface by way of a corrugated metal sheet (U.S. Pat. No. 4,398,077). These devices are all cooking utensils. By contrast, the invention is concerned with disposable packaging, typically formed from paper and plastic film.
Laminated sheets known as susceptors have been previously proposed for heating foods with microwave energy by absorbing a portion of the microwave energy and transferring it by conduction to a food product. In some cases sheet material of this kind from which the susceptor is formed is stiff, brittle, subject to breakage, and not adapted for use in lightweight packaging products which should be disposable and low in cost. In other cases the laminated susceptors, while interacting with the microwave energy present in an oven, do not adequately heat the food product. Still other laminates can heat only one side of the food product. So, for example, if the food product is rectangular in shape, two or more sides remain unheated.
The application of heat to at least two sides of each piece of food, and most preferably to all sides, is highly beneficial because it has been found that when a food piece such as a french fried potato is placed in an ordinary paperboard carton and heated in a microwave oven, the potato pieces become soggy. This occurs even if an effort is made to allow steam to vent from openings at the top of the package. As a result, attempts have been made to develop susceptors for lining food cartons to augment the heat provided by direct microwave interaction with the food For example, U.S. Pat. Nos. 4,612,431 and 4,735,513 describe laminates comprised of polyester to which thin, semiconductive layers of metal have been applied. These laminates are bonded to a wall of the package for absorbing microwave energy and transferring the energy to the food product as heat. Tests have shown, however, that these laminates and the resulting packages are not effective in crisping, browning or toasting the surface of foods such as french fried potatoes where there are numerous pieces of food present in the package. Thus, after heating, the products are perceived to be moist, limp and soggy.
Other attempts have been made to deal with the problem of crisping the surface of a food product. For example, U.S. Pat. Nos. 4,267,420 and 4,230,924 provide a lightweight flexible wrapper formed from a laminate composed of a flexible sheet material that interacts with microwave energy. One major shortcoming is that food sticks have to be individually wrapped and later unwrapped one-by-one by the consumer. Another problems results from the fact that portions of the sheet material, when unsupported, can shrivel, shrink, split and crack, particularly in areas where it is not in contact with the food.
U.S. Pat. Nos. 4,935,592 and 5,084,601 address the objectives of 1) providing a microwave interactive laminate or susceptor as a sheet of material that will crisp, toast or brown several surfaces of a stick-shaped food product such as french fried potatoes, fish sticks and the like so that after heating it is perceived to be crisp and appetizing to the consumer; and 2) configuring this microwave interactive sheet material within a package to furnish a plurality of compartments that will each enclose individual food pieces, and particularly food in stick form such as french fried potatoes or the like, snugly enough to contact or almost contact and heat the food pieces on all major sides but yet hold the food pieces sufficiently loose to allow the food pieces to be easily removed.
The package described in U.S. Pat. No. 5,084,601, while very good, is somewhat complicated and expensive to manufacture and has been perceived by consumers to contain too much packaging material. Therefore, one major objective of the present invention is to provide a simpler and lower cost package that uses less material, is lighter in weight to serve as a disposable package suitable for heating individual servings of stick or log shaped foods such as french fried potatoes, fish sticks, egg rolls, bread sticks or waffle sticks in a microwave oven and for browing, crisping or toasting the surface of each food piece.